Anticorrosive paint



Patented Aug. 20, 1946 2,406,307 7 ANTICORROSIVE PAINT Norman John Read,Greenford, England, assignor to Goodlass Wall & Lead Industries Limited,Oxted, Surrey, England No Drawing. Application March 9, 1945, Serial e 9Claims.

This invention relates to lead pigment paints, particularly for theprotection of iron and steel. It is well known that certain pigmentsused in oil paints exhibit marked anti-corrosive 'efi'ects In GreatBritain February 11,

tially the whole of the lead present in the form of combined PbO2 notonly when the proportions of oxides used correspond to those requiredfor the production of the ortho-plumbate but also upon iron and steel.when they approximate to those required for the I have now found thatthose plumbates 0f the production of the meta-plumbate, and maytherealkaline earth metals, in which substantially all fore be regardedas a plumbate intermediate beof the lead is in the form of lead peroxidecomtween ortho and meta, or a mixture of ortho and bined with analkaline earth metal oxide have meta. very desirable pigmentaryproperties, particularly The constitution of the alkaline earth metal inprotecting iron and steel against corrosion. plumbates is not at presentfully understood, but They have also been found to have the desirableonly those plumbates in which at least 90% by properties of highobliterating power, good staweight of the lead present is in the form ofcomi i y in p int f m a l b orp ion val e bined PbOz are suitable for mypurpose, and I which permit the manufacture of paints of high 5 preferto employ plumbates in which more than pigment content. 90% of the leadis in the form of combined PbOz. These pigments range in colour fromsubstan- This is because any uncombined PbOz tends to tially white,through buff and chocolate to black. revert to PhD, and the presence ofany consid- Thus for example, barium plumbatain addition erableproportion of free P130 in the material to its protective value,providesa new black pigcauses the manufactured paint to stiffen andbement completely inorganic in composition and come unuseable; sucheffect of free P100 in lead of such an oil absorption that relativelyhighly paints is well known. pigmented paints can be made from it. ThisI find that when the plumbates are manufaccharacteristic is particularlyvaluable in the protured by the above-indicated process, and carriedduction of flat black paints. out at a temperature of around 750 C., there- The invention accordingly provides a paint, sulting productconsists, except in the case of comprising as a pigment constituent aplumbate barium plumbate, of a fine soft powder suitable of an alkalineearth metal, in which substantially for direct incorporation in paints.the whole of the lead is in the form of lead per-- The alkaline earthmetal plumbate according oxide combined with an oxide of an alkalineearth to the invention can be employed in conjunction metal. with otherpigments, e. g. iron oxide, to improve I prefer to manufacture thealkaline earth the protective value of the latter against cormetalplumbate by the known reaction which rosion. Thus small proportions ofcalcium consists in heating together in air an oxide of plumbatein anotherwise not anti-corrosive pigthealkaline earth metal (or a saltthereof such ment mixture have been found to confer antias a nitrate, acarbonate or the like which will corrosive properties. produce an oxideof the alkaline earth metal on Whereas calcium plumbate as generallypreheating) and an oxide of lead, e. g. litharge or pared has a buficolour, a modified form of red lead, or a salt of lead which willproduce a c lcium plumbate h vin a substantially White lead oxide orlead oxides on heating. 40 colour can be prepared, according to the in-My experiments as so far conducted have vention, by adding to themixture of lead oxide shown that, in the case of calcium and strontiumand calcium oxide before furnacing a small proplumbates, the proportionsof alkaline earth portion of the order of 0.5% to 5.0% of powmetal oxideand lead oxide should approximate dered silica and furnacing at atemperature of to those required theoretically for the production about700 C. At lower temperatures the reof the ortho-plumbate Ca2PbO4, andthat if the proportions are such as to approach those requiredtheoretically for the production of the meta-plumbate CaPbOs, aconsiderable proportion of the lead in the resulting product is not inthe form of PbO2 combined'with the alkaline earth metal oxide and thematerial is unsuitable for use as a pigment. Surprisingly enough,however, this does not apply in the case of the product from the heatingtogether of B20 and PbO, or compounds which produce these oxides onheating. The material so obtained contains substanaction is unduly slow,while if the temperature is too high the resulting product tends to havea brown colour.

A White calcium plumbate pigment can also be obtained by employing anexcess of calcium oxide during the heating operation.

Pigments so made can then be made into paints having a high obliteratingpower and good weathering properties which are specially suitable forprotective purposes when applied to bare iron or steel.

Owing to the high protective power of these plumbate pigments and theirgreat opacity in oil vehicles they can be used with advantage with largeamounts of extender pigments to produce cheaper paints of goodprotective value and considerable hiding power. Some extenders may beproduced in admixture with the plumbate as the result of the heatingoperation, these either arising from incomplete decomposition of thesalt of the alkaline earth metal or being added during or prior to theheating operation. Other extenders are more suitably admixed with theplumbate after the production thereof, e. g. during or afterincorporation of the plumbate in a suitable vehicle.

Paints according to the invention, in addition to affording goodprotection for iron and steel against atmospheric conditions, also giveexcellent protection in the severe conditions of intermittent alternateimmersion in fresh or salt water and exposure to the air.

The following are typical examples of the manufacture of alkali metalplumbates containing substantially the whole of the lead in the form ofcombined PbOz.

I. CALCIUM PLUMBATE 17.6 parts by weight of commercial precipitatedbarium carbonate were heated in air with 10 parts by weight of lithargeat 750 C. for 8 hours.

The resulting product was in the form of a black friable cake which whenground gave a product suitable for incorporation in a paint.

(D) From mixtures containing equimolecular proportions of barium oxideand lead oxide.

8.8 parts by weight of commercial precipitated barium carbonate wereheated in air with 10 parts by weight of litharge at 750 C. for 8 hours.

The resulting product was in the form of a black friable cake which whenground gave a product suitable for incorporation in a paint.

The following are examples of typical paints according to the invention:

Example 1 The paint consists of 70 parts by weight of calcium plumbatemixed with 30 parts by weight of a vehicle made up of:

Parts by weight Refined linseed oil 47 Pale boiled linseed oil 47 Cobaltnaphthenate liquid driers 5 Example 2 The paint consists of 64 parts byweight of calcium plumbate mixed with 36 parts by weight of a vehiclemade up to contain:

Parts by weight Linseed stand oil (30 poises) 34 Pale boiled linseed oil25.5 Mineral spirit 33.8 Cobalt naphthenate liquid driers 5.8 Aluminiumstearate 0.9

Example 3 Barium plumbate parts by weight mixed with 30 parts by weightof a vehicle made up of Example 4 Barium plumbate paint with 30% bariumcarbonate as extender in the pigment. The extender being introduced inthe furnacing operation.

The paint consists of:

7 Parts by weight Barium plumbate 49 Barium carbonate 21 Vehicle 30 Thevehicle is of the same composition as that used in Example 2.

Example 5 Example of use of calcium plumbate in mixture with anotherpigment to improve its rust inhibitive qualities.

The paint consists of:

Parts by weight Red iron oxide 55.2

Calcium plumbate 13.8 Vehicle 31 The vehicle consists of:

7 Parts by weight Refined linseed oil 42 Pale boiled linseed oil 42IWineral spirit 6.3

Cobalt naphthenate liquid driers 9.7

Example 6 Parts by weight Calcium plumbate 51.2 Barytes (paint makingquality) 13.0 Vehicle 35.8

The vehicle is of the same composition as that used in Example 2.

What I claim as my invention and desire to secure by Letters Patent is:

1. An anti-corrosive oil paint comprising as a vehicle constituent aglyceride drying oil and as iii a pigment constituent, a plumbate of analkaline earth metal in which substantially the whol of the lead ispresent as lead peroxide combined with an alkaline earth metal oxide.

2. An anti-corrosive paint comprising, in admixture, glyceride dryingoil vehicle and a plumbate of an alkaline earth metal in which at leastby weight of the lead is present as lead peroxide combined with analkaline earth metal oxide.

3. An anti-corrosive paint comprising, in admixture, glyceride dryingoil vehicle, a plumbate of an alkaline earth metal in which at least 90%by weight of the lead is present as lead peroxide combined with analkaline earth metal oxide and another pigment.

4. An anti-corrosive oil paint comprising as a vehicle constituent aglyceride drying oil and as a pigment constituent an admixture of bariumplumbate and barium carbonate, at least 90% 0t 5 the lead in saidbariumplumbate being present as lead peroxide combined with barium oxide.

5. An anti-corrosive oil paint comprising as a vehicle constituent aglyceridedrying oil and as a pigment constituent an admixture of calciumplumbateand barytes, at least 90% of the lead in said calcium plumbatebeing present as lead peroxide combined with calcium oxide.

6. An anti-corrosive oil paint comprising as a vehicle constituent aglyceride drying oil and as a pigment constituent an admixture of analkaline earth metal plumbate'and iron oxide, at least 90% of the leadin said plumbate being present as lead peroxide combined with analkaline earth metal oxide.

'7. An anti-corrosive paint comprising, in ad-,

15 silica.

mixture, a linseed oil vehicle and a plumbate of an alkaline earth metalin which at least 90% by weight of the lead is present as lead peroxidecombined with an alkaline earth metal oxide.

8. An anti-corrosive oi-l paint as defined in claim 2 in which thepigment constituent is white calcium plumbate obtained by heating leadoxide with an excess of calcium oxide in air at a ternperature of about700 C.

9. An anti-corrosive oil paint as defined in claim 2 in which thepigment constituent is a white calcium plumbate obtained by heating leadoxide and calcium oxide in air at a temperature of about 700 C. in thepresence of a. small proportion, of the order of 0.5% to 5%, of powderedNORMAN dorm READ.

